Polymer precursors of polyacetylene. Thermal degradation of poly(vinyl esters). Part 1-Molecular weight dependence of the autocatalytic thermal degradation of poly(vinyl acetate) (PVAc)

This study is the first of a series on the pyrolyses of poly(vinyl esters) in which the kinetics of the isothermal degradation up to high conversions of five unfractionated heterotactic samples of poly(vinyl acetate) (PVAc) ranging in viscosity-average molecular weight Mv from 3·7 × 104 to 2·4 × 105 has been investigated by a static procedure in a nitrogen atmosphere over a wide temperature range. The experimental results can be explained by assuming the occurrence of a catalyzed deacetylation reaction which is first order with respect to CH3COOH simultaneously with an uncatalyzed reaction. This kinetic model, based on the stripping mechanism, has been shown to be in very good agreement with the experimental data not only for low, but also for moderately high, degrees of conversion. Rate constants k1 and k2, Arrhenius parameters E and A and ΔS≠ values have been determined for both the autocatalyzed and uncatalyzed elimination reactions. They are reasonable, since they compare quite favorably with those taking place by a unimolecular dissociation mechanism in homogeneous gas-phase reactions of simple ester molecules which we can consider as model substances for our stripping elimination reaction. The dependence of the kinetic parameters of the samples on molecular weight has been interpreted. © 1988.Peer Reviewe

NMR studies of the structure and dynamics of polymer gels based on N-isopropylacrylamide (NiPAAm) and methacrylic acid (MAA)

Full Paper: A series of copolymer gels and interpenetrating networks (IPN) based on N-isopropylacrylamide (NiPAAm) and methacrylic acid (MAA) were synthesized and subsequently investigated by magic angle spinning H-1 MAS, cross polarization C-13 CP-MAS and pulse-saturation transfer C-13 PST-MAS NMR. The structure of the interpenetrating networks is compared to that of the copolymer gels with the same composition. The study of the proton lines reveals low mobility of the chains in the copolymer gels and IPN with higher concentration of MAA, whereas those which are predominantly NiPAAm show higher mobility and therefore narrower proton lines. C-13 CP-MAS revealed an interaction between the components of the IPNs. The PST-MAS technique was utilized to study the structure of the polymers in the gel phase. Copolymer gels exhibit some additional peaks in the carbonyl region due to the new chemical environment in the stereoregular sequences. In order to assure assignment, uncrosslinked copolymers with similar compositions as the copolymer gels were synthesized for comparative purposes and examined by conventional solution- state C-13 NMR. A linear homopolymer of NiPAAm was synthesized inside of a P(MAA) gel. The polymer was extracted after the completion of the reaction and characterized by solution C-13 NMR. About 24% of this P(NiPAAm) homopolymer could not be extracted presumably because of a strong hydrogen bonding or partial topological constrains. In the C-13 NMR spectrum a new signal appeared in the carbonyl region due to MAA monomeric units. It may correspond to the methacrylic carbonyls interacting by hydrogen bonds with the amide groups